New Planet Definition Enlarges Solar System

The International Astronomical Union (IAU) has crafted a new definition for what constitutes a planet that would expand the solar system to Pluto and beyond, encompassing 12 bodies in all.

Earlier this year, a special team convened by the IAU struggled to establish the criteria that defines a planet. Various proposals included size (mass) and orbit. On the second morning several members admitted that they had not slept well, worrying that we would not be able to reach a consensus, writes Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics and chair of the Planet Definition Committee. But by the end of a long day, the miracle had happened: we had reached a unanimous agreement.

The new proposed definition of a planet is: a celestial body with sufficient mass to assume a nearly spherical shape that orbits a star without being another star or a satellite of another planet. By this definition, the list of planets in order from the sun now reads: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto-Charon (considered a double-planet system) and the newly discovered and officially unnamed 2003 UB₃₁₃, otherwise known as Xena.

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